Laser material machining using hybrid processes

ABSTRACT

In a method for machining workpieces by combining a first machining tool with at least one second machining tool, wherein at least one of the first and second machining tools employs laser radiation, the first machining tool is operated with a first pulse modulation and the at least one second machining tool is operated with a second pulse modulation. The first and second pulse modulations are synchronized. Same pulse frequencies can be used for the first and second pulse modulations, or, in the alternative, pulse frequencies are used that are an integral multiple relative to one another, wherein the first and second pulse modulations are in a fixed or variably controlled phase relationship relative to one another.

The invention relates to a method for the machining of materials bycombining one machining tool with at least one additional machiningtool, wherein at least one machining tool employs laser radiation.

Such methods and devices for material machining, in which at least onemachining tool in the form of a laser beam is used in combination withother machining tools, for example, laser beams and/or electric arcsand/or plasma beams and/or one or several other energy or particlebeams, for example, flame, cutting tools, water jet, electron beams, areknown. As representative examples in this context, publications, patentapplications, and patents of Fraunhofer ILT concerning so-calledlaser-electric arc hybrid welding can be referenced.

The hybrid technology is based on the combination of laser beam weldingwith metal shielding gas welding of metals, in the following referred toas MSG, i.e., metal inert gas welding, in the following referred to asMIG, or metal active gas welding, in the following referred to as MAG,or with tungsten inert gas welding in the following referred to as TIG.

In this connection, reference is being had to the following patents:

-   -   Nozzle arrangement for simultaneous welding with laser beam and        electric arc (DE 196 27 803 C1);    -   Method for welding workpieces (DE 195 00 512);    -   Method for welding workpieces with laser radiation (EP 0 800 434        B1).

In the following examples of the prior art, the depth welding effect ofthe focused laser radiation is combined with additional energy and, inthe case of shielding gas welding, also with additional material supplyfrom an electric arc. Additional energy and possibly additional materialserve, for example, for bridging the joining gaps or for compensatingedge displacement. The effectiveness, the productivity, and the qualityof the hybrid process are superior to the properties of the individualprocesses.

A further possibility uses the combination of different laser beamsources, for example, strongly focused CO₂ laser radiation with diodelaser radiation having larger, for example, linear or annular, activesurfaces, in order to achieve a preheating or post-heating of thematerial or an enlargement of the melted volume and, accordingly, abetter degassing thereof; compare, for example, S. Bouss, B. Brenner, E.Beyer: Innovations in laser hybrid technology; Industrial LaserSolutions; January 2001, Penn Well. Also, one patent of Fraunhofer ILTemploys for consumption-stabilized flame cutting the combination ofseveral laser beams or the combination of laser radiation with otherenergy sources (DE 41 15 561 C2).

Moreover, when exclusively being used for material machining or inhybrid combination with other tools, methods of laser material machiningas well as electric arc processes, for example, MIG/MAG or TIG,currently employ occasionally already the possibility of pulsemodulation for a temporal control of the machining process. Certainlaser source types, however, are not able to perform in permanentoperation; they can also can only be used in pulsed operation.

Pulse modulation of radiation, electric arc, plasma or other energy,pulse, or particle sources, for example, flame, cutting tools, waterjet,electric beam, serve, for example, the following purposes in theindividual processes:

-   -   targeted influencing of interaction time,    -   metered and portioned energy introduction,    -   metered, portioned material removal (for example, during        percussion drilling),    -   gentle material machining with reduced heat-affected zone by        employing short pulse-on and pulse-off times,    -   safe droplet removal (MSG),    -   improved material transition (MSG),    -   minimization of spatter,    -   process stabilization in otherwise instable working areas, for        example, exothermic over reaction during flame cutting with heat        build-up, unsteady transition arc during inert gas welding in        medium current intensity range,    -   increase of energy flux density in the pulse for average current        density and path energy that are reduced or identical in        comparison to permanent operation, and    -   short-term increase of processing temperature and/or evaporation        proportion in the interactive zone.

In the presently known technologies, primarily the limitations regardingthe possibility of affecting the degree of coupling of the individualmethods when combining them to a hybrid process have been perceived as adisadvantage.

In the past, for determining the degree of coupling primarily thespacing or the degree of overlap of the active area has been used. Inorder to reinforce, for example, coupling of laser beams and electricarc, their roots on the workpiece have been moved closer together. Inorder to suppress the coupling, the roots are moved apart from oneanother. However, at the same time, the size and shape of theinteraction geometry and the effective reaction time are changed; incertain situations this can be very disadvantageous. This will beexplained in more detail with the aid of some examples.

Especially when using CO₂ lasers, care must be taken to avoid plasmashielding of the laser radiation in the electric arc or plasma. However,at the same time, guiding and/or concentration of the electric arc bythe focused laser beam is desirable. Accordingly, goals are present thatnegatively affect one another.

The same can hold true for the combination, for example, of thewavelength of different laser radiations, when, for example, a strongcoupling, on the one hand, is advantageous for utilizing theabsorption-increasing effect on the workpiece, for example, bygenerating periodic surface structures, but, on the other hand, a strongcoupling leads to disruptions of at least one of the methods, forexample, in that its laser radiation is absorbed or scattered by thematerial vapor above the workpiece caused by the other laser radiation.

It is an object of the invention to provide a method and a device of theaforementioned kinds that enables with technically simple means to makethe degree of coupling, and optionally also the coupling type, of theeffect of the individual methods in the employed hybrid technologyelectronically adjustable in a targeted and variable way.

This object is solved for a method of the aforementioned kind inaccordance with the invention in that a synchronized modulation, i.e.,synchronous or a synchronous modulation, of the first machining tool iscarried out when combining it with the additional machining tool that isalso pulse-modulated.

According to the invention, the degree of coupling and optionally alsothe coupling type become adjustable in a targeted and variable wayelectronically without mechanical adjustments on the tool for the effectof the individual methods in the employed hybrid technology, primarilywithout mandatorily having to use a change of the local spacing of theinteractive areas of the individual methods on or within the workpieceand without having to abandon space adjustments that may be useful forother reason, for example, the spacing zero. The tool components aretherefore synchronized in a targeted way.

According to one embodiment of the invention, it is provided that thefirst machining tool and the at least one additional machining tool aremodulated with the same pulse frequence or with pulse frequencies thatare an integral multiple relative to one another and that their pulsemodulations are in a fixed or variably controlled or governed phaserelation to one another.

A particularly simple control of the modulation is provided when thepulse control signals of at least one pulse-modulated machining tool areused as master signal for triggering a synchronized control of the pulsemodulation of at least one additional machine-tool in slave operation.

In order to be able to react faster and also simpler to changes in theprocess course and also for the input, it is advantageous when the phaserelationship is controlled and/or governed as a function of and/or foraffecting one or several process parameters and/or as a function ofsensor signals.

A further embodiment of the invention provides that in-phasesynchronization is carried out. However, it is also possible that anantiphase synchronization is carried out.

A particularly simple synchronization can be achieved when the slavepulse is generated at the beginning or the end of the master pulse orvice versa.

Moreover, it is provided that individual pulses or pulse packages aregenerated.

Moreover, it is advantageous when the controllable radiation, which isoptionally not externally controlled, i.e., not from outside the toolcontrol, or the machining tool or the process-controlled machining toolthat is internally process-controlled by variable pulse frequency is themaster. The lafter, for example, can be used for modern digital currentsources of electric arc processes or rotating cutting tools, forexample, milling tools, whose rotary frequency is to be understood inthis context as the pulse frequency.

Moreover, it is provided that the additional machining tool is a laserdevice and/or an electric arc radiation device and/or a plasma radiationdevice and/or one or several other energy, pulse, or particle sources.

A further advantageous method is provided in that the machining ofworkpieces can be selected from the following list:

-   -   separation or removal methods, in particular, cutting, drilling,        material removal, perforations, scoring, engraving, structuring,        or cleaning;    -   joining methods, in particular, welding, soldering or bonding,    -   coating and building processes, in particular, coating,        generating, selective sintering, or rapid prototyping,    -   surface treatment and surface finishing, in particular,        hardening, refining, alloying, dispersing, polishing and        applying lettering, shaping, and bending,        wherein the combination of the machining tools is configured        such that their active areas that can be exposed optionally to        effects of different kinds, on or within the workpiece overlap        or adjoin one another immediately during the machining process.

Moreover, the object is solved for a device of the aforementioned kindin accordance with the invention by a first pulse generator formodulation of the laser radiation, by a second pulse generator formodulation of the additional machining tool, and by a synchronizer for asynchronous modulation of the combination.

Advantageous embodiments of the device according to the invention aredetailed in the dependent claims. Since these dependent claimscorrespond essentially to the dependent claims that further define themethod, a detailed description thereof is not provided here.

Further features and advantages of the invention result from thefollowing description of several embodiments as well as the drawings towhich reference is being had. It is shown in:

FIG. 1 a block diagram of a master-slave triggering action for thesynchronization of the pulse modulation with fixed or controlled phaserelationship; and

FIG. 2 several diagrams as examples for characteristic phaserelationships for synchronized pulse modulation in hybrid processes.

Based on FIGS. 1 and 2, methods and devices for hybrid processing ofmaterials by combining a machining tool with at least one additionalmachining tool will be explained, wherein at least one machining toolemploys laser radiation.

In FIG. 1, schematically a device 10 for hybrid processing of materialsby a machining tool in combination with at least one additionalmachining tool is illustrated. The device 10 comprises in theillustrated embodiment a first pulse generator 12 for modulation of alaser radiation as a machining tool. Moreover, the device 10 comprises asecond pulse generator 14 for modulation of the additional machiningtool 12.

Between the first pulse generator 12 and the second pulse generator 14 asynchronizer 16 is connected that, in the device 10 illustrated in FIG.1, receives output values of the first pulse generator 12 and inputs, inturn, output values into the second pulse generator 14. Moreover, thesynchronizer 16 receives input values that are illustrated in FIG. 1 bya dotted line.

Furthermore, the first pulse generator 12 also supplies output values tothe first source 20 that, in the illustrated embodiment, is used as amaster signal. In some cases, it can be more advantageous to employ thesource 22 of the additional machining tool as a master.

In a similar way, the second pulse generator 14 provides output valuesto a second source 22 that, in the illustrated embodiment, is used as aslave signal for the slave operation.

Accordingly, by means of the first and the second sources 20 and 22,pulse control signals of at least one pulse generator 12 are processedas a master signal for triggering a synchronous control of the pulsemodulation of the pulse control signals of the at least one additionalpulse generator 14 in slave operation.

As indicated in FIG. 1, there are input devices for process parametersas well as sensors for process results for controlling and/or governingthe phase relationship as a function of and/or for affecting one orseveral process parameters and/or as a function of sensors signals.

The output signals of the first source 20 and of the second source 22,respectively, are employed for the process operation; this is indicatedin FIG. 1 by the box “process” identified by reference numeral 24.

The above-mentioned sensor signals are supplied to a controller 18 thatis connected, in turn, to an input device and accordingly also to thesynchronizer 16 through the input device.

The first and second pulse generators 12 and 14 and the synchronizer 16are therefore designed to modulate the laser radiation and the at leastone additional machining tool by pulse frequencies that are an integralmultiple relative to one another and put the pulse modulations of thefirst and second pulse generators 12 and 14 in a fixed or in variablephase relationship variably controlled or governed by the controller 18.

Inter alia, the synchronizer 16 can also be designed for an in-phasesynchronization. It is also possible to design the synchronizer 16 foran antiphase synchronization. Finally, there is also the possibility touse the synchronizer 16 for generating a slave pulse at the beginning orthe end of the master pulse or vice versa.

In this connection, the first and second pulse generators 12 and 14 canbe designed such that they generate individual pulses and/or pulsepackages.

In FIG. 2, several diagrams as examples for characteristic phaserelationships for synchronized pulse modulation in hybrid methods areillustrated. The diagram referenced at a) represents the modulation ofthe master. The diagram b) represents the in-phase slave modulation.

The diagram c) shows that it is also possible to employ slave modulationwith minimal phase displacement, in this case displaced by t_(c). Thismeans that a finite temporal overlap of the pulse-on times occurs butcan also mean a common pulse drop time together with the master for ashorter pulse-on time of the slave. Finally, the diagram d) provides anantiphase slave modulation. This provides no temporal overlap of thepulses; the pulses however can also follow in direct sequence. In thediagram d) there is a phase displacement of t_(d).

In general, it can be stated that a targeted adjustment of the processcycle by adjusted synchronization is possible. Examples of the processcycle are courses over time of temperature, natural voltage, reaction,material application, material removal, material bonding, materialseparation, as well as phase transition.

A strong coupling, i.e., an in-phase synchronized pulse modulation,effects an improvement of the depth welding effect of the laser, animprovement of the pinch effect for droplet removal of the MIG processas well as an improvement of the electric arc guiding and contraction bymeans of a focused laser.

A decoupling, i.e., an antiphase synchronized modulation, hasadvantageous effects on preventing laser beam shielding and/orscattering and/or refraction within the electric arc plasma. Thetemporal separation and thus capillary formation and droplet removalwith material transfer during laser-MIG hybrid welding are possible alsoin this connection.

Also possible is an adjusted coupling, i.e., a targeted phasedisplacement of the synchronous pulse modulation of one tool componentor of a radiation. Examples for this are threshold-dependent partialprocesses that only upon reaching or surpassing a process thresholdbecome effective with the corresponding phase-delayed post-pulse bymeans of the pre-pulse of the other tool component or the at least oneadditional radiation. The phase delay is varied in this connection foroptimizing the type of action, the efficiency, the productivity, thestability, as well as the quality of the hybrid process.

The additional machining tool can be a laser radiation and/or anelectric arc radiation and/or a plasma radiation and/or one or severalother energy, pulse, or particle sources.

In the following several effects will be described, in particular, thepre-pulsing by a laser, pre-pulsing by an electric arc or plasma beam aswell as post pulsing.

The effects of pre-pulsing by a laser are as follows:

-   -   preheating, for example, for improved wettability of materials        or for metallurgical adjustment of the process,    -   cleaning,    -   layer removal,    -   pre-ionization,    -   chemical activation,    -   pre-melting (preprocessing).

The effects and results of pre-pulsing by an electric arc or plasma beamare as follows:

-   -   preheating,    -   absorption increase for the laser beam by surface changes, for        example, by changing the temperature, structure, material,        and/or by chemical reaction,    -   absorption increase for the laser beam by changing the        atmosphere near the surface and thus the relative refractive        index,    -   portioned energy and material supply, for example, for bridging        joining gaps.

Post-pulsing can have the following effects or results:

-   -   post-heating,    -   surface finishing by supplying energy or material,    -   degassing of the melt during welding and coating,    -   material removal or material joining after preparation by a        pre-pulse,    -   chemical reaction, for example, joining or separating, after        pretreatment by a pre-pulse.

Moreover, it is possible to modulate the following parameters,

-   -   output,    -   current,    -   voltage,    -   speed, for example, of the wire feed of the additional material        or the electrode that is being consumed,    -   frequency.

The parameters of modulation can be of the following type:

-   -   basic level,    -   pulse frequency,    -   pulse length, pulse pause, or pulse-width repetition,    -   pulse peak value,    -   duration of the pulse peak value,    -   temporal course of the pulse rise,    -   temporal course of the pulse drop.

The invention thus provides the degree of coupling and optionally alsothe type of coupling for the effect of the individual methods inemployed hybrid technology and enables variable adjustmentelectronically without mechanical adjustment of the tool. Primarilywithout mandatorily having to use a change of the local spacing of theinteractive areas of the individual methods on or within the workpieceand without having to abandon space adjustments that may be useful forother reason, for example, the spacing zero. Moreover, it is possible,where it is advantageous, to increase the coupling past the level thatis already provided alone by complete overlapping of the interactivezones or the identical roots of the individual processes on or withinthe workpiece. On the other hand, the invention also makes possible inthis configuration a substantial decoupling of individual processes,inasmuch as this is desirable for the hybrid process effect.

List of Reference Numerals

-   -   10 device    -   12 first pulse generator    -   14 second pulse generator    -   16 synchronizer    -   18 controller    -   20 first source    -   22 second source    -   24 process

1.-21. (canceled)
 22. A method for machining workpieces by combining afirst machining tool with at least one second machining tool, wherein atleast one of the first and second machining tools employs laserradiation, the method comprising the steps of: operating the firstmachining tool with a first pulse modulation and the at least one secondmachining tool with a second pulse modulation; and synchronizing thefirst and second pulse modulations of the first machining tool and theat least one second machining tool.
 23. The method according to claim22, wherein in the step of synchronizing same pulse frequencies are usedfor the first and second pulse modulations, wherein the first and secondpulse modulations are in a fixed or variably controlled phaserelationship relative to one another.
 24. The method according to claim22, wherein in the step of synchronizing pulse frequencies are used thatare an integral multiple relative to one another, wherein the first andsecond pulse modulations are in a fixed or variably controlled phaserelationship relative to one another.
 25. The method according to claim22, wherein in the step of synchronizing one of the first and at leastone second machining tools is used as a master and the other or othersof the first and at least one second machining tools are slaves, whereinpulse control signals of the master are used as a master signal forsynchronizing the first and second pulse modulations.
 26. The methodaccording to claim 23, wherein the phase relationship is controlled as afunction of one or several process parameters and/or for affecting oneor several process parameters and/or as a function of sensor signals.27. The method according to claim 24, wherein the phase relationship iscontrolled as a function of one or several process parameters and/or foraffecting one or several process parameters and/or as a function ofsensor signals.
 28. The method according to claim 22, wherein the stepof synchronizing is carried out by in-phase synchronization.
 29. Themethod according to claim 22, wherein the step of synchronizing iscarried out by antiphase synchronization.
 30. The method according toclaim 25, wherein a slave pulse in response to the master pulse isgenerated at the beginning or at the end of the master pulse, or viceversa.
 31. The method according to claim 22, further comprising the stepof generating individual pulses or pulse packages for the first andsecond pulse modulations.
 32. The method according to claim 25, whereinthe master is a machining tool that is optionally not externallycontrollable.
 33. The method according to one claim 25, wherein themaster is a machining tool that is internally process-controlled withvariable pulse frequency.
 34. The method according to claim 22, whereinthe at least one second machining tool employs at least one of laserradiation, electric arc radiation, plasma radiation, an energy source, apulse source, and a particle source.
 35. The method according to claim22, wherein the first and second machining tools are selected from thegroup consisting of separating tools, material removing tools, joiningtools, coating tools, building tools, surface treatment tools, andsurface finishing tools, wherein the first and at least one secondmachining tools are configured such that active areas during machiningon or within the workpiece overlap or adjoin one another immediatelyduring the machining process.
 36. The method according to claim 35,wherein the first and second machining tools perform machining processesselected from the group consisting of cutting, drilling, materialremoving, perforating, scoring, engraving, structuring, cleaning,welding, soldering, bonding, coating, generating, selective sintering,rapid prototyping, hardening, refining, alloying, dispersing, polishing,applying lettering, shaping, and bending.
 37. A device for hybridprocessing of materials by a first machining tool in combination with atleast one second machining tool, wherein the first machining toolemploys laser radiation, the device comprising: a first pulse generatorfor pulse modulation of the laser radiation of the first machining tool;a second pulse generator for pulse modulation of the at least one secondmachining tool; a synchronizer for synchronous modulation of the firstand the at least one second machining tool.
 38. The device according toclaim 37, further comprising a controller, wherein the first and secondpulse generators and the synchronizer are designed to modulate the laserradiation and the at least one additional machining tool with same pulsefrequencies, wherein the pulse modulations of the first and second pulsegenerators are in a fixed or variable phase relationship that isvariably controlled by the controller.
 39. The device according to claim37, further comprising a controller, wherein the first and second pulsegenerators and the synchronizer are designed to modulate the laserradiation and the at least one additional machining tool with pulsefrequencies that are an integral multiple relative to one another,wherein the pulse modulations of the first and second pulse generatorsare in a fixed or variable phase relationship that is variablycontrolled by the controller.
 40. The device according to claim 37,further comprising at least one source for processing pulse controlsignals generated by the first pulse generator as a master signal fortriggering a synchronous control of the modulation of pulse controlsignals of the second pulse generator in slave operation.
 41. The deviceaccording to claim 37, further comprising at least one source forprocessing pulse control signals generated by the second pulse generatoras a master signal for triggering a synchronous control of themodulation of pulse control signals of the first pulse generator inslave operation.
 42. The device according to claim 37, furthercomprising input devices for process parameters and sensors for processresults in the form of sensor signals, wherein the input devices and thesensors are configured to control a phase relationship of the pulsemodulations as a function of the process parameters and/or for affectingone or several of the process parameters and/or as a function of thesensors signals.
 43. The device according to claim 37, wherein thesynchronizer provides in-phase synchronization.
 44. The device accordingto claim 37, wherein the synchronizer provides antiphasesynchronization.
 45. The device according to claim 37, wherein thesynchronizer generates a slave pulse at the beginning or at the end ofthe master pulse.
 46. The device according to claim 37, wherein thefirst and second pulse generators generate individual pulses and/orpulse packages.
 47. The device according to claim 37, wherein the atleast one second machining tool employs at least one of laser radiation,electric arc radiation, plasma radiation, an energy source, a pulsesource, and a particle source.